Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $96.65   5.154%   $101.6313   $101.63   $101.65   $101.60  
  Purchase #2 $228.82   6.128%   $242.8421   $242.84   $242.85   $242.80  
  Purchase #3 $86.76   9.842%   $95.2989   $95.30   $95.30   $95.30  
  Purchase #4 $192.93   7.633%   $207.6563   $207.66   $207.65   $207.70  
  Purchase #5 $223.79   7.815%   $241.2792   $241.28   $241.30   $241.30  
  Purchase #6 $213.34   3.874%   $221.6048   $221.60   $221.60   $221.60  
  Purchase #7 $173.55   5.523%   $183.1352   $183.14   $183.15   $183.10  
  7 purchase totals = $1,215.84       $1,293.4478   $1,293.45   $1,293.50   $1,293.40